Anaphylatic reactions are severe, generalized clinical reactions. They can occur with or without warning, progress rapidly from isolated to systemic symptoms, and may in some cases result in death. Estimates in the United States have projected that anaphylaxis can occur in approximately one in every 3000 hospitalized patients, and may be responsible for more than 500 deaths annually. This review will present information related to the epidemiology, pathophysiology, diagnosis and treatment of anaphylactic reactions. In addition, key prevention measures will be discussed.